1. Field of the Invention
The subject invention pertains to a factory or offsite prefabricated drive conversion unit for the technical renovation of an existing escalator, with which, during the local modification work, the old handrail drive and its peripheral parts are replaced without changing the existing basic structure of the escalator.
2. Discussion of the Background of the Invention and Material Information
The handrail drive of an escalator is a technically demanding assembly. Its main task or object consists of the gentle guiding and tensioning as well as synchronous driving, relative to the stair movement, of the handrail. For the care of the handrail as well as for achieving the longest possible service life, the frictional forces, specifically produced by the drive unit, should not be excessive due to the danger of crushing or deformation, and the bending or deflection angles, due to the accompanying overload of the handrail edges, should not be too tight or narrow. In addition, the operation thereof should occur with the use of small tension forces, which in turn increases the degree of effectiveness of the drive and which contributes to the care or protection of the entire system. Old, existing handrail drive systems generally cannot meet the noted requirements and show, even after a relatively short service time, corresponding wear patterns. With an otherwise generally good operating condition of an escalator, it is therefore worthwhile to replace the handrail drive unit with a conversion or exchange construction which, at the same time, permits the upgrading thereof to new standards and requirements.
Generally, two different drive methods or principles are utilized, one pertaining to the pressing of the handrail, with a partial envelopment, onto a large friction wheel, the other pertaining to the passage of the handrail through a plurality of linearly arranged friction and control roller pairs which also frictionally drive the handrail.
The first-noted principle permits that, in addition to the handrail drive, the clamping device can be arranged within the same arrangement, which makes the addition of a second peripherally placed tensioning assembly superfluous.
U.S. Pat. No. 3,651,919 to Vollmer describes and shows a handrail drive of the previously noted type. The lower part of the escalator utilizes a friction wheel which is enveloped by the handrail over an angle of about 90.degree. and is pressed thereagainst by a tensioned roller chain. Located on each side of the driving wheel, in order to maintain the angle of envelopment, are fixedly attached turn around or return elements, each utilizing three rollers. An additional device, arranged at the upper portion of the escalator, is utilized for the tensioning of the handrail.
The turn around elements of this device bend the handrail strongly backwards and the separate tensioning device additionally adds to the cost of the drive. It is obvious that this handrail drive can be improved via an exchange or conversion unit which utilizes the advantages of a modern, technical drive.
The firm of John P. SPRIGGS, Home Elevators Inc., Roswell, Ga., U.S.A., is marketing a handrail drive exchange or conversion unit, U.S. Pat. No. 5,427,221, which includes, in a common carrier unit, a friction wheel with a pressing device having turn around and guide rollers on both sides thereof. Therein, the handrail, both before and after the pressing device, runs over but a single roller, so that the handrail suffers from high wear due to the severe deviation thereof. In addition, the outer guidance causes frictional markings or grooves in the turn around rollers.